U.S. patent application number 10/922032 was filed with the patent office on 2005-03-03 for surface acoustic wave device and method for manufacturing the same.
Invention is credited to Akiyama, Kenji, Sakaguchi, Kenji.
Application Number | 20050046307 10/922032 |
Document ID | / |
Family ID | 34197192 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050046307 |
Kind Code |
A1 |
Sakaguchi, Kenji ; et
al. |
March 3, 2005 |
Surface acoustic wave device and method for manufacturing the
same
Abstract
A surface acoustic wave device includes a piezoelectric
substrate, an interdigital transducer (IDT) electrode, and a
connecting portion that is electrically connected with the IDT
electrode. The surface acoustic wave device further includes a
wiring portion, a portion of which is disposed on the connecting
portion, and a bump disposed on the wiring portion. The connecting
portion includes a comb-shaped portion at an end of the connecting
portion on which the wiring portion is disposed.
Inventors: |
Sakaguchi, Kenji;
(Komatsu-shi, JP) ; Akiyama, Kenji; (Shiga-ken,
JP) |
Correspondence
Address: |
Keating & Bennett LLP
Suite 312
10400 Eaton Place
Fairfax
VA
22030
US
|
Family ID: |
34197192 |
Appl. No.: |
10/922032 |
Filed: |
August 19, 2004 |
Current U.S.
Class: |
310/313D |
Current CPC
Class: |
H03H 9/059 20130101 |
Class at
Publication: |
310/313.00D |
International
Class: |
H03H 009/25 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 2, 2003 |
JP |
2003-310342 |
Jul 15, 2004 |
JP |
2004-209035 |
Claims
What is claimed is:
1. A surface acoustic wave device comprising: a piezoelectric
substrate; an interdigital transducer (IDT) electrode disposed on
the piezoelectric substrate by a lift-off method; a connecting
portion electrically connected with the IDT electrode; and a wiring
portion disposed on the connecting portion; wherein the IDT
electrode and the connecting portion are formed at the same time;
and a comb-shaped portion is provided at an end of the connecting
portion on which the wiring portion is disposed.
2. The surface acoustic wave device according to claim 1, wherein a
space between combs of the comb-shaped portion is about 5 .mu.m or
less.
3. The surface acoustic wave device according to claim 1, wherein a
space between combs of the comb-shaped portion is the same as a
spacing width of the IDT electrode.
4. The surface acoustic wave device according to claim 1, wherein
the IDT electrode and the connecting portion have a thickness of
about 200 nm or more.
5. The surface acoustic wave device according to claim 1, wherein
the piezoelectric substrate is a LiTaO.sub.3 substrate.
6. The surface acoustic wave device according to claim 1, wherein
the IDT electrode includes a Ti layer and a Cu--Al layer disposed
on the Ti layer.
7. The surface acoustic wave device according to claim 6, wherein
the Ti layer has a thickness of about 10 nm and the Cu--Al layer
has a thickness of about 400 nm.
8. A surface acoustic wave device comprising: a piezoelectric
substrate; an interdigital transducer (IDT) electrode disposed on
the piezoelectric substrate by a lift-off method; a connecting
portion electrically connected with the IDT electrode; and a wiring
portion disposed on the connecting portion; wherein the IDT
electrode and the connecting portion are formed at the same time;
and a fine irregular-shaped portion having an irregularity of about
5 .mu.m or less is provided at an end of the connecting portion on
which the wiring portion is disposed.
9. The surface acoustic wave device according to claim 8, wherein
the IDT electrode and the connecting portion have a thickness of at
least about 200 nm.
10. The surface acoustic wave device according to claim 8, wherein
the piezoelectric substrate is a LiTaO.sub.3 substrate.
11. The surface acoustic wave device according to claim 8, wherein
the IDT electrode includes a Ti layer and a Cu--Al layer disposed
on the Ti layer.
12. The surface acoustic wave device according to claim 11, wherein
the Ti layer has a thickness of about 10 nm and the Cu--Al layer
has a thickness of about 400 nm.
13. A method for manufacturing a surface acoustic wave device
comprising the steps of: preparing a piezoelectric substrate;
forming an IDT electrode and a connecting portion that is
electrically connected with the IDT electrode on the piezoelectric
substrate by a lift-off method; and forming a wiring portion on the
connecting portion; wherein the step of forming the connecting
portion includes a step of forming a comb-shaped portion at an end
of the connecting portion on which the wiring portion is
formed.
14. The method for manufacturing a surface acoustic wave device
according to claim 13, wherein in the step of forming the
comb-shaped portion, a space between combs of the comb-shaped
portion is about 5 .mu.m or less.
15. The method for manufacturing a surface acoustic wave device
according to claim 13, wherein in the step of forming the
comb-shaped portion, a space between combs of the comb-shaped
portion is the same as a spacing width of the IDT electrode.
16. The method for manufacturing a surface acoustic wave device
according to claim 13, wherein the IDT electrode and the connecting
portion are formed to have a thickness of about 200nm or more.
17. The surface acoustic wave device according to claim 13, wherein
the IDT electrode are formed to include a Ti layer and a Cu--Al
layer disposed on the Ti layer.
18. The surface acoustic wave device according to claim 17, wherein
the Ti layer has a thickness of about 10 nm and the Cu--Al layer
has a thickness of about 400 nm.
19. A method for manufacturing a surface acoustic wave device
comprising the steps of: preparing a piezoelectric substrate;
forming an IDT electrode and a connecting portion that is
electrically connected with the IDT electrode on the piezoelectric
substrate by a lift-off method; and forming a wiring portion on the
connecting portion; wherein the step of forming the connecting
portion includes a step of forming a fine irregular-shaped portion
having an irregularity of about 5 .mu.m or less at an end of the
connecting portion on which the wiring portion is formed.
20. The surface acoustic wave device according to claim 19, wherein
the IDT electrode and the connecting portion are formed to have a
thickness of at least about 200 nm.
21. The surface acoustic wave device according to claim 19, wherein
the IDT electrode are formed to include a Ti layer and a Cu--Al
layer disposed on the Ti layer.
22. The surface acoustic wave device according to claim 21, wherein
the Ti layer has a thickness of about 10 nm and the Cu--Al layer
has a thickness of about 400 nm.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a surface acoustic wave
device including at least one interdigital transducer (IDT)
electrode formed by a lift-off method and at least one connecting
portion that is electrically connected with the IDT electrode, and
in particular, to a surface acoustic wave device further including
at least one wiring portion disposed on the connecting portion and
a method for manufacturing the same.
[0003] 2. Description of the Related Art
[0004] In recent years, surface acoustic wave devices assembled by
a flip-chip bonding system have been widely used in order to reduce
the size of surface acoustic wave devices. In this flip-chip
bonding system, at least one bump is disposed on at least one pad
area in a surface acoustic wave device. The surface acoustic wave
device is bonded with at least one connecting area disposed on, for
example, a package through the bump. Thus, the surface acoustic
wave device is electrically connected and mechanically bonded with
the package.
[0005] The bump used in the flip-chip bonding system provides not
only electrical connection of the surface acoustic wave device to
the package but also mechanical fixing of the surface acoustic wave
device to the package. Therefore, sufficient bonding strength is
required between the bump and the pad area in the surface acoustic
wave device. In general, in order to increase the bonding strength
between the bump and the pad area, the film thickness of the pad
area is increased.
[0006] In the surface acoustic wave device, an IDT electrode
disposed on a piezoelectric substrate and a connecting portion
electrically connected with the IDT electrode are formed at the
same time by a lift-off method. Therefore, the connecting portion
has the same film thickness as that of the IDT electrode portion.
In order to form a bump having sufficient bonding strength, another
layer having a predetermined pattern is formed on the connecting
portion.
[0007] When the IDT electrode, having a fine pattern, is formed by
the lift-off method, a resist pattern for forming the IDT electrode
is formed such that the cross-section of opening areas
corresponding to the fine pattern tapers from the substrate surface
to the upper surface of the resist.
[0008] Also, the resist pattern of the connecting portion, which is
rougher than the IDT electrode, is formed such that the
cross-section of opening areas tapers from the substrate surface to
the upper surface of the resist. However, as a result of subsequent
heat treatment such as baking, the above-described taper, i.e., a
reverse-tapered shape, cannot be maintained in the connecting
portion having the rough pattern. Consequently, after the resist
pattern and unnecessary electrode films are removed by the lift-off
method, for example, burring of an electrode occurs at an end of
the connecting portion.
[0009] Furthermore, another layer having a predetermined pattern is
formed on the connecting portion in order to form the bump.
Unfortunately, for example, the above-described electrode burring
causes a problem such as disconnection on the other layer.
[0010] In order to solve the above-described problem, Japanese
Unexamined Patent Application Publication No. 2002-261560 discloses
the following surface acoustic wave device. The above-described
patent document discloses a surface acoustic wave device and a
method for manufacturing the same including the steps of forming a
connecting portion of a surface acoustic wave element, and
subsequently performing etching such that an end surface of the
connecting portion has a stair-like shape.
[0011] However, the surface acoustic wave device and the method for
manufacturing the same according to the above-described related art
have the following problem.
[0012] According to the above-described patent document, a
connecting portion of a surface acoustic wave element is formed,
and etching is then performed such that an end surface of the
connecting portion has a stair-like shape. In this process, a
resist pattern in which the end of the connecting portion
corresponds to an opening area is formed on the surface acoustic
wave element having the connecting portion thereon. Subsequently, a
portion of the end surface of the connecting portion is removed by,
for example, submerging the element in an etchant. The resist
pattern is then removed to form the desired pattern. The formation
of this resist pattern includes the following steps. A resist
having a predetermined film thickness is applied, the resist layer
is exposed with a photo-mask having a predetermined pattern, and
the resultant resist layer is then developed. Unfortunately, this
method includes many steps.
SUMMARY OF THE INVENTION
[0013] In order to overcome the problems described above, a surface
acoustic wave device according to a preferred embodiment of the
present invention includes a piezoelectric substrate, an
interdigital transducer (IDT) electrode formed on the piezoelectric
substrate by a lift-off method, a connecting portion electrically
connected with the IDT electrode, and a wiring portion disposed on
the connecting portion, wherein the IDT electrode and the
connecting portion are formed at the same time, and a comb-shaped
portion is provided at an end of the connecting portion on which
the wiring portion is disposed.
[0014] The space between combs of the comb-shaped portion is
preferably about 5 .mu.m or less. The space between combs of the
comb-shaped portion is preferably substantially the same as the
spacing width of the IDT electrode.
[0015] A surface acoustic wave device according to another
preferred embodiment of the present invention includes a
piezoelectric substrate, an IDT electrode formed on the
piezoelectric substrate by a lift-off method, a connecting portion
electrically connected with the IDT electrode, and a wiring portion
disposed on the connecting portion, wherein the IDT electrode and
the connecting portion are formed at the same time, and a fine
irregular-shaped portion having an irregularity of about 5 .mu.m or
less is provided at an end of the connecting portion on which the
wiring portion is disposed.
[0016] The IDT electrode and the connecting portion preferably have
a thickness of at least about 200 nm.
[0017] A method for manufacturing a surface acoustic wave device
according to another preferred embodiment of the present invention
includes the steps of preparing a piezoelectric substrate, forming
an IDT electrode and a connecting portion that is electrically
connected with the IDT electrode on the piezoelectric substrate by
a lift-off method, and forming a wiring portion on the connecting
portion, wherein the step of forming the connecting portion
includes a step of forming a comb-shaped portion at an end of the
connecting portion on which the wiring portion is formed.
[0018] A method for manufacturing a surface acoustic wave device
according to another preferred embodiment of the present invention
includes the steps of preparing a piezoelectric substrate, forming
an IDT electrode and a connecting portion that is electrically
connected with the IDT electrode on the piezoelectric substrate by
a lift-off method, and forming a wiring portion on the connecting
portion, wherein the step of forming the connecting portion
includes a step of forming a fine irregular-shaped portion having
an irregularity of about 5 .mu.m or less at an end of the
connecting portion on which the wiring portion is formed.
[0019] In the surface acoustic wave device according to preferred
embodiments of the present invention and the method for
manufacturing the same, a connecting portion that does not have
electrode burring at an end thereof is provided in the surface
acoustic wave device.
[0020] Therefore, problems such as disconnection on, for example, a
wiring portion disposed on the connecting portion does not occur.
Consequently, the present invention provides a surface acoustic
wave device having greatly improved reliability.
[0021] These and various other features, elements, steps,
characteristics and advantages of the present invention will become
more apparent from the following detailed description of preferred
embodiments thereof with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a schematic plan view of a surface acoustic wave
device according to a preferred embodiment of the present invention
(first preferred embodiment);
[0023] FIG. 2 is a partial enlarged plan view showing the example
of the surface acoustic wave device according to the preferred
embodiment of the present invention (Example 1); and
[0024] FIG. 3 is a partial enlarged plan view showing an example of
a surface acoustic wave device according to another preferred
embodiment of the present invention (second preferred
embodiment).
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0025] First Preferred Embodiment
[0026] A first preferred embodiment of the present invention will
now be described in detail with reference to the attached
drawings.
[0027] FIG. 1 is a schematic plan view of a surface acoustic wave
device according to a first preferred embodiment of the present
invention, and FIG. 2 is a schematic enlarged plan view showing
portion A in FIG. 1.
[0028] Referring to FIG. 1, a surface acoustic wave device 50
includes a piezoelectric substrate 1, interdigital transducer (IDT)
electrodes 2, and connecting portions 3 that are electrically
connected with the IDT electrodes 2. The surface acoustic wave
device 50 further includes wiring portions 4, a portion of which is
disposed on the connecting portions 3, and bumps 5 disposed on the
wiring portions 4.
[0029] In FIG. 2, a portion that is not the top layer is shown by a
broken line.
[0030] As shown in FIG. 2, a connecting portion 3 is disposed on
the piezoelectric substrate 1. A wiring portion 4 is disposed on a
portion of the connecting portion 3. The connecting portion 3
includes a comb-shaped portion 6 at an end of the connecting
portion 3 on which the wiring portion 4 is disposed.
[0031] A method for manufacturing the above surface acoustic wave
device 50 according to the first preferred embodiment of the
present invention will now be described in detail.
[0032] First, a resist having a desired thickness is applied on the
piezoelectric substrate 1 such as a LiTaO.sub.3 substrate with, for
example, a spin coater. The piezoelectric substrate 1 is not
limited to the LiTaO.sub.3 substrate. Other substrates such as
quartz crystal, LiNbO.sub.3, and Li.sub.2B.sub.4O.sub.7 substrates
may be used according to the desired piezoelectricity.
[0033] Subsequently, the resist is exposed with a mask for
photolithography having a predetermined pattern corresponding to
the IDT electrodes 2, the connecting portions 3, and the
comb-shaped portions 6. The resist is then developed to form the
resist pattern having the desired opening areas. In view of a
lift-off method, the resist pattern is formed such that the
cross-section of the opening areas tapers from the substrate
surface to the upper surface of the resist.
[0034] The resist pattern is then subjected to post-baking.
[0035] Subsequently, to form electrodes for the surface acoustic
wave device, a first layer (about 10 nm) of Ti is formed on the
piezoelectric substrate 1 having the above resist pattern.
Furthermore, a second layer (about 400 nm) of Al-1 weight percent
Cu is formed thereon.
[0036] The piezoelectric substrate 1 is then submerged and shaken
in a remover to remove the resist pattern and any unnecessary
electrode film. Thus, the IDT electrodes 2 and the connecting
portions 3 that are electrically connected with the IDT electrodes
2 are formed by the lift-off method. In this preferred embodiment,
the line width and the spacing width of the IDT electrodes 2 are
about 1 .mu.m. The titanium used as the first layer functions as a
contact metal to provide adhesiveness.
[0037] Subsequently, the wiring portions 4 are formed. A first
layer (about 200 nm) of Ni--Cr, and a second layer (about 800 nm)
of Al are formed as the wiring portions 4 by the lift-off method.
Since this lift-off method is the same as the above described
method, the detailed description thereof is omitted.
[0038] The bumps 5 are then formed on the wiring portions 4. The
bumps 5 are formed at a location where the films Al--Cu/Ti, which
are the IDT electrodes 2 and the connecting portions 3, are not
disposed thereunder. Gold bumps or solder bumps are used as the
bumps 5.
[0039] A wiring portion 4 is formed on a connecting portion 3
including a side of the connecting portion 3, the connecting
portion 3 being electrically connected with an IDT electrode 2 and
having a rough shape as compared to the shape of the IDT electrode
2. A comb-shaped portion 6 is disposed at an end of the connecting
portion 3 on which the wiring portion 4 is formed. In the
comb-shaped portion 6 of this preferred embodiment, the line width
is about 1 .mu.m, the spacing width is about 1 .mu.m, and the
length is about 5 .mu.m. The spacing width of the comb-shaped
portion 6 is preferably about 5 .mu.m or less, and is substantially
the same as the spacing width in the pattern of the IDT electrode
2. The length of the comb-shaped portion 6 is preferably about 1 to
about 10 .mu.m. The comb-shaped portion 6 is preferably formed at
the same time as the IDT electrode 2 and the connecting portion
3.
[0040] As described above, the surface acoustic wave device 50 is
produced.
[0041] In general, when a pattern of, for example, an electrode is
formed by the lift-off method, as described above, the shape of the
resist pattern is formed in view of the lift-off method. In the
lift-off method, the resist pattern is formed such that the
cross-section of the opening area corresponding to the pattern of,
for example, the electrode tapers from the substrate surface to the
upper surface of the resist. The formed resist pattern is subjected
to thermal shrinkage due to subsequent post-baking.
[0042] The IDT electrode portion wherein the resist pattern has a
fine shape is not substantially affected by thermal shrinkage.
Therefore, the fine resist pattern maintains the above-described
taper. On the other hand, the connecting portion in which the shape
of the resist pattern is rougher than the shape of the resist
pattern in the IDT electrode is substantially affected by thermal
shrinkage due to the post-baking. Accordingly, the resist pattern
cannot maintain the above-described taper at the opening area
corresponding to the rough pattern.
[0043] In the lift-off method, the cross-sectional shape of the
opening area in the resist pattern significantly affects the shape
of the electrode pattern that is formed thereafter. In a resist
pattern having a preferable cross-sectional shape at the opening
area, the unnecessary electrode films and the resist are removed.
Subsequently a desired electrode pattern shape is formed. This is
because the above-described taper at the cross-section of the
opening area enables the electrode pattern that is formed and the
unnecessary electrode films to be discontinuous. In contrast, in
the area where the above-described taper cannot be maintained, the
electrode pattern that is formed and the unnecessary electrode
films are continuous. Therefore, the unnecessary electrode films
are torn from the electrode pattern during removal. Consequently,
for example, electrode burring is formed in the electrode
pattern.
[0044] The reason for this is as follows. In a fine resist pattern,
since the stress caused by thermal shrinkage is dispersed by the
fine pattern, the stress does not substantially change the shape of
the pattern. On the other hand, in a rough resist pattern, since
the stress caused by thermal shrinkage is not dispersed, the stress
substantially changes the shape of the pattern.
[0045] When the wiring portion is formed on the connecting portion
having the electrode burring, the electrode burring causes
problems, such as disconnection at the formed wiring portion.
[0046] However, in the above-described preferred embodiment, the
comb-shaped portion having the shape similar to that of the IDT
electrode is disposed at an end of the connecting portion on which
the wiring portion is formed. Accordingly, a resist pattern which
maintains the above-described taper is formed without being
affected by thermal shrinkage. Consequently, this structure enables
the desired IDT electrode and the connecting portion to be
formed.
[0047] In particular, when a resist pattern for forming an IDT
electrode and a connecting portion having a film thickness of at
least about 200 nm is formed, the above-described advantage is
achieved.
[0048] According to the above-described preferred embodiment of the
present invention, the comb-shaped portion having a shape similar
to that of the IDT electrode is disposed at an end of the
connecting portion on which the wiring portion is formed.
Therefore, as described above, a resist pattern which maintains the
above-described taper is formed without being affected by thermal
shrinkage. The shape is not limited to the above-described
comb-shape. Alternatively, a fine irregular-shaped portion that has
an irregularity of about 5 .mu.m or less may be disposed at an end
of the connecting portion. This fine irregular-shaped portion also
provides the same advantage.
[0049] In a second preferred embodiment as shown in FIG. 3, a
connecting portion 3 is disposed on a piezoelectric substrate 1. A
wiring portion 4 is disposed on a portion of the connecting portion
3. The connecting portion 3 includes a fine irregular-shaped
portion 7 having a wave shape and disposed at an end of the
connecting portion 3 on which the wiring portion 4 is provided. In
the fine irregular-shaped portion 7, each of width 7a and height 7b
of the irregularity is about 5 .mu.m or less. In a fine resist
pattern having a fine irregular-shaped portion 7, since the stress
caused by thermal shrinkage is dispersed by the fine pattern, the
stress does not substantially change the shape of the pattern.
[0050] Accordingly, in such a fine resist pattern, the
above-described taper is maintained in the cross-section. The
electrode pattern that is formed and the unnecessary electrode
films are not continuous, and therefore, the unnecessary electrode
films are not torn from the electrode pattern during removal.
Consequently, for example, the electrode burring is not formed in
the remaining electrode pattern.
[0051] The shape of the fine irregular-shaped portion 7 having an
irregularity of about 5 .mu.m or less and shown in FIG. 3 may have
any shape such as a serration, a semicircle, or a semiellipse as
long as the irregularity is about 5 .mu.m or less. These shapes of
the fine irregular-shaped portion 7 also provide the same
advantage.
[0052] It should be understood that the foregoing description is
only illustrative of the present invention. Various alternatives
and modifications can be devised by those skilled in the art
without departing from the present invention. Accordingly, the
present invention is intended to embrace all such alternatives,
modifications and variations that fall within the scope. of the
appended claims.
* * * * *